Presentation on theme: "Chapter 38 Viruses Objectives Define viruses Consider whether they are living or non-living Describe the structure of a virus List the names of the virus."— Presentation transcript:
1 Chapter 38 VirusesObjectives Define viruses Consider whether they are living or non-living Describe the structure of a virus List the names of the virus shapes Describe how replication occurs in viruses Explain the medical importance of viruses to humans, plants and animals.
2 Viruses Tiny (They are much smaller (50 times) than a bacterium. Need Electron Microscope to see themNon Cellular (not made of cells)Cannot reproduce on their own (not alive according to our rules)
3 Structure of Viruses A virus consists of: A strand of genetic material either DNA or RNA.A protein coat capsid.Viruses do not have ribosomes, mitochondria or other cell organelles.
4 Viruses do not respire.They cannot reproduce outside a host cell.They are obligate parasites
5 Viruses are not living organisms? Non-livingPossess genetic material either DNA or RNAAre non-cellularPossess a protein coatCannot reproduce by themselvesCan replicate (inside a living cell)Only have one type of nucleic acid (living things have both DNA and RNA)
7 RNA or DNA? Viruses with RNA Viruses with DNA Human immunodeficiency virus (HIV)Influenza virusesRabiesViruses with DNAWartsChickenpoxmononucleosis
8 ShapesViruses can be:SphericalRod shapedComplex shaped
9 BacteriophageA bacteriophage or phage is a virus that infects bacteriaBacteriophages are among the best studied viruses. T phage takes about30 minutes to replicate.
10 Virus Replication Attachment Proteins on the virus match up with the wall of the host cellEntryThe virus forms a hole and the viral DNA is injected into the bacteriaSynthesisThe host DNA is switched off and the viral DNA takes over.It makes virus parts.AssemblyThe virus parts are put together and new viruses are made.ReleaseThe host cell bursts and releases thousands of the viruses.These move to other cells.
11 The chart below shows the replication of a bacteriophage The chart below shows the replication of a bacteriophage. This virus infects bacteria.It takes about 30 minutes to complete its replication cycle.
13 Benefits of Viruses (need to know two harmful examples and one beneficial example of viruses) Genetic EngineeringViruses can be used to transfer genes from one organism to another in genetic engineering. Such viruses are called vectorse.g. human insulin gene transferred into E. coli2. Control of infectionsBacteriophages may be used to control bacterial infections
14 Disadvantages of Viruses 1. Human DiseasesViruses cause many diseases inHumans e.g. colds, influenza,measles and cold sores2. Plant DiseasesViruses cause many plant diseasesincluding potato mosaic disease
15 Viruses can be beneficial… Bacteriophages – attack & destroy bacteriaBaculovirus – ebola-like virus that attacks insectsCould use for pest control in cropsCabbage loopers eatcabbage cropsVirus can kill pests in days(it’s really gross)… and then there are those that are not so good….
16 Control & ImmunityViruses are controlled by body’s general defence system e.g. skinImmunity to many viral infections can be produced -by vaccinations or by injecting anti-biodies into the body.Antibiotics kill bacteria and fungi but have no effect on viruses.
17 InterferonInterferon is a range of substances produced by virus infected cells to protect healthy cells.Interferon can be made artificially now and can be used to treat colds etc.
18 Viruses Enter Living Cells Viruses enter bacterial cells by punching a hole in the cells wall and injecting its DNA
19 Mutating virusesViruses can mutate when they copy the genetic materialCopy something wrongMistake proves usefulMore powerful virus (more infectious)Viruses don’t mutate often, except…Influenza & HIV
20 Retroviruses Retroviruses contain RNA instead of DNA They have an enzyme that converts the Virus RNA to DNAHIV is a Retrovirus
21 Plant Diseases Caused by Viruses Potato Mosaic Virus
22 HIV VirusAIDS: Acquired Immune Deficiency Syndrome is caused by the HIV virusEffects: The virus damages the lymphocyte white blood cells making them unable to make antibnodies to fight against other diseases e.g. colds.A person suffering from AIDS is unable to fight infections and may die from diseases e.g. cancer or pneumonia.Spread: Spread through body fluids e.g. bloodUnprotected sex with an infected person or drug users sharing needlesTreatment: Drugs are given to slow down the progression of AIDS but there is no cure.
24 How Is HIV Spread? Sexual contact Sharing contaminated needles Blood transfusionsBreast feeding (mother to baby)Mother to baby during pregnancy or birth
25 There are approx. 14,000 new cases of HIV worldwide every day FACTSIn the US, there is better than a 1/1000 chance of contracting HIV during unprotected sexA person can be contagious for more than 10 years before any sign of the disease is apparentHIV becomes AIDS when the number of immune cells drops below a predetermined numberNo one dies from HIV or AIDS; people die from secondary infections (ranging from the common cold to cancer)More than 3 million people (size of Chicago) die each yearThere are approx. 14,000 new cases of HIV worldwide every day